Numerous systems have been developed in recent years for increasing the amount of heat transfer from a stove or fireplace to a room in order to reduce total heating requirements by the home heating plant. These devices have typically been provided in the form of andirons or grates having blowers for establishing a stream of heated air from the stove or fireplace to the room to thereby heat the room by convection. This approach has substantially increased the heating efficiency of conventional stoves and fireplaces since, in the absence of such devices, heat transfer between a stove or fireplace and room is principally by radiation. Radiation constitutes only about five percent of the heat generated by the fuel, the remainder being wasted through the chimney.
One type of andiron design of the prior art, as shown in Hamilton U.S. Pat. No. 4,018,208, has included a hollow, C-shaped andiron through which air is blown. Heat transfer to the forced air is principally at the interface between the air and inner wall surface of the andiron. In order to increase the heat transfer from the hollow andiron to the air stream, Young et al. U.S. Pat. No. 4,078,542 has proposed filling a hollow grate with a sheet metal, fin matrix. The fin matrix structure, however, has been found to be difficult to manufacture. Also, it has been observed that there is a tendency for ashes and particulate matter to be recirculated into the grate through the blower and to accumulate on the fins, thereby reducing the amount of air flowing through the system. The fin type matrix is difficult to thereafter clean, and any crimping of the fin structure during cleaning permanently decreases air flow and reduces the efficiency of heat transfer to the room.
The fin type heat exchange structure, although having a high surface area-to-volume ratio which does efficiently transfer heat to the air stream, is not capable of storing a substantial amount of heat. After combustion of the fuel has been completed, therefore, no substantial amount of heat can be drawn from the fins for continued heat transfer to the room.